1. Field of the Invention
The present invention relates to a secondary battery including a hydroxide-ion-conductive ceramic separator.
2. Description of the Related Art
Zinc secondary batteries, such as nickel-zinc secondary batteries and zinc-air secondary batteries, have been developed and studied over many years. Unfortunately, these batteries have not yet been put into practice. This is due to a problem that zinc contained in the negative electrode forms dendritic crystals, i.e. dendrites, during a charge mode of the battery and the dendrites break the separator to cause short circuit between the negative electrode and the positive electrode. Thus, a strong demand has arisen for a technique for preventing the short circuit caused by dendritic zinc in zinc secondary batteries, such as nickel-zinc secondary batteries and zinc-air secondary batteries.
In order to meet such a demand, batteries including hydroxide-ion-conductive ceramic separators have been proposed. For example, Patent Document 1 (WO2013/118561) discloses a nickel-zinc secondary battery including a separator composed of a hydroxide-ion-conductive inorganic solid electrolyte between a positive electrode and a negative electrode for preventing the short circuit caused by dendritic zinc, wherein the inorganic solid electrolyte is a layered double hydroxide (LDH) having a basic composition represented by the formula: M2+1-xM3+x(OH)2An−x/n·mH2O (wherein M2+ represents at least one type of divalent cation, M3+ represents at least one type of trivalent cation, An− represents an n-valent anion, n is an integer of 1 or more, and x is 0.1 to 0.4). Patent Document 2 (WO2013/073292) discloses a zinc-air secondary battery including a separator composed of a layered double hydroxide (LDH) having the same basic composition as that in Patent Document 1 and disposed on one surface of the air electrode for preventing a short circuit caused by dendritic zinc between the positive and negative electrodes during a charge mode of the battery and also preventing the intrusion of carbon dioxide into the electrolytic solution.
Patent Document 3 (WO2013/161516) discloses an application of a hydroxide-ion-conductive ceramic separator to a battery other than a zinc secondary battery; specifically, a lithium-air secondary battery including, as an anion exchanger, an inorganic solid electrolyte composed of a layered double hydroxide (LDH) having the aforementioned basic composition. According to this patent document, the anion exchanger can prevent the intrusion of carbon dioxide into the battery.
Known techniques for improving the air tightness of an alkaline battery involve the application of an adhesive to a separator and a battery can. For example, Patent Document 4 (JP2009-123378) discloses a cylindrical alkaline battery including an isolator that covers an opening of the bottom of a separator to isolate a negative electrode mixture from the bottom of a positive electrode can, wherein the isolator is composed of a cured product of a hot-melt resin primarily containing an olefin copolymer. Patent Document 5 (JPH10-172525) discloses an alkaline battery including a cylindrical metal can filled with a positive pole generator and a negative pole generator that are isolated by a separator, and an insulating gasket fixed to a rod collector disposed at the center of the negative pole generator so as to seal the metal can, wherein an epoxy adhesive is applied to a contact portion between the insulating gasket and the upper portion of the inner wall of the separator.